1. Field of the Invention
The present invention relates to a system for improving hydrophilicity of a contact lens and application of the system to packaging of the contact lens, and more particularly to a technique for advantageously improving the hydrophilicity of the contact lens while advantageously packaging the contact lens for marketing the contact lens.
2. Description of Related Art
One of conventional dissatisfactions most commonly felt by contact lens users (consumers) is dryness of the eye while wearing the contact lens. Thus, in order to improve the contact lens itself, it has been considered to use a contact lens material having a high degree of water retaining property, or to employ a treatment process for improving the hydrophilicity of the surface of the contact lens. It has also been considered to add a component having a high degree of moisture retaining property to a contact lens preserving solution or other solution to be used in contact with the contact lens, in order to improve the hydrophilicity of the surface of the contact lens for thereby mitigating the dryness of the eye.
In the field of cosmetics, various compounds have been proposed as the component having a high degree of moisture retaining property. Among such compounds, a hyaluronic acid is a well known compound having an extraordinary high degree of water retaining property per one molecule. Particularly, a high-molecular weight hyaluronic acid is preferably used since it has a structure in which, one molecule has multiple water retaining portions, and which can exhibit an excellent water retaining property. Conventionally, a natural hyaluronic acid derived from the combs of chickens is used, and this natural hyaluronic acid is the high-molecular weight hyaluronic acid having a molecular weight of not lower than one million. Accordingly, the hyaluronic acid is generally recognized as the high-molecular weight hyaluronic acid.
In the field of a contact lens solution, some proposals have been made to utilize a viscosity increasing effect and anionic nature of the hyaluronic acid (see Patent Documents 1 to 5, for example). However, most of the proposals are intended to use the high-molecular weight hyaluronic acid, and in their embodiments, contact lens solutions are prepared by using the high-molecular weight hyaluronic acid having a molecular weight of not lower than one million. Some of the proposals indicate that it is possible to use the hyaluronic acid having a wide range of molecular weight, such as a high-molecular weight of not lower than one million, a molecular weight of not higher than 100,000, and a low-molecular weight of not higher than 10,000. However, there is disclosed nothing about the effects of the hyaluronic acids having such different molecular weights with respect to the contact lens. Particularly, the high-molecular weight hyaluronic acid has an excessively high degree of viscosity increasing effect, such that when a small amount of the high-molecular weight hyaluronic acid is added to the contact lens solution, the viscosity of the solution is rapidly increased. As a result, there are inherent risks that the desired hydrophilicity given by the hyaluronic acid cannot be imparted to the contact lens, and the hyaluronic acid has adverse influences on the user's feeling (sense of use) while wearing and scrubbing the contact lens, and on an effect of cleaning the contact lens. Further, none of the documents refer to a relationship between the effect of imparting the hydrophilicity to the contact lens and a number of molecules (molar concentration) of the hyaluronic acid.
On the other hand, the contact lens is preserved in a liquid medium such as an isotonic sodium chloride solution after the contact lens is produced until it is supplied to the consumer (user). Namely, the contact lens is accommodated in a suitable sealable container, together with the liquid medium such as the isotonic sodium chloride solution used as a packaging solution (wrapping solution or preserving solution for distribution), and the container is sealed with the contact lens being immersed in the liquid medium. The sealed container is shipped from a manufacturer as a contact lens packaging product to be supplied to the user (see Patent Documents 6 and 7). The contact lens accommodated in the suitable sealable container is immersed in the packaging solution and sterilized by heating before the contact lens is shipped and supplied to the user. Where the high-molecular weight hyaluronic acid is added to the packaging solution in order to impart a desired viscosity to the solution, the viscosity of the solution decreases due to the above-described heat sterilization treatment, giving rise to a problem that the sense of use and initial wearing comfort of the contact lens are deteriorated when the contact lens is supplied to and used by the user.